Mine galleries are open areas underground which result from the underground excavation of minerals, such as coal. Mines typically have a number of galleries at various depths from the surface. Galleries are accessed by elevators from the surface, tracks, or haulage ways. Pillars of rock and minerals, typically twenty feet wide by fifty feet long, are left within the galleries in spaced-apart relation to define roof or ceiling supports in the galleries. In coal mines, the galleries are typically formed with three to eight foot ceilings and the pillars are approximately twenty feet apart. The gallery increases in size through the excavation and removal of rock and minerals. The excavation face in the gallery is thereby located farther from the mine entrance. All equipment, supplies, materials, and personnel enter and exit the gallery through the elevator, track, or haulage ways. The demands on the entrance ways accordingly may be significant, depending on the depth of the mine, the number of galleries, the number of miners and other workers, and the activity in the mine.
Fresh cool air is needed at the excavation face for the miners and other workers. The fresh air is communicated from an intake, across the working face, and out of the mine through a return. To control air flow and reduce the demands on the volume of air required, the gaps between adjacent pillars are walled-ir to define separate passageways. There are various types of barriers used to form walls in galleries. A number of barriers have been previously described for blocking off mine entries or other types of underground passageways. For example, U.S. Pat. No. 4,077,474 to Hattori discloses a curtain of fire-resistant fabric releasable from a frame above an entry. U.S. Pat. No. 3,831,318 to Richmond discloses a series of inflatable bags which, when inflated with air, converge together to block the opening or passageway. Similarly, U.S. Pat. Nos. 4,102,138 and 4,036,024 to Dreker disclose an inflatable bag, initially filled with air, which is later filled with a material of a type which permanently blocks the mine passageway. U.S. Pat. No. 3,645,337 to Livingston discloses an overhead chamber through which a gel is excreted to form a curtain of synthetic material which dries into a solid blockade. U.S. Pat. No. 4,023,372 to Preslar discloses a partially inflatable wall of fabric which allows passage therethrough. U.S. Pat. No. 4,277,204 to Koppers and U.S. Pat. No. 4,983,077 to Sorge disclose the use of self-supporting forms filled with hardenable material to support the roof of the mines.
A current technology typically used to form walls, commonly called "stoppings" and "seals", to block mine openings and close the gaps between pillars, are constructed of conventional concrete or cinder blocks. These are usually stacked without mortar, and have a resistant coating applied to the exposed surfaces of the blocks to bond the blocks together. This construction technique is allowed under The US Code of Federal Regulations (CFR) which requires stoppings to have the "structural equivalent to an 8-inch, hollow-core, concrete block stopping with mortared joints." (Mine Safety & Health Administration Report 07-183-93 (Jul. 2, 1993).
While providing a satisfactory stopping, the concrete block walls have drawbacks. Construction of such stoppings are time and labor intensive, and each stopping wall typically requires eight to ten, or more, manhours to construct. Each wall requires a large number of blocks, which must be brought into the mine through the entrance to the gallery. The workers who assemble the stoppings also must travel into the mine through the elevator, track, or haulage ways. These materials and the workers involved place overhead demands on the mine entrance way and increase mine costs which are not directly related to excavation of minerals.
Stoppings must provide the equivalent critical properties to that of concrete blocks as defined by 30 CFR Part 75.333 with respect to durability, noncombustibility and surface flammability:
1) one hour fire resistance as described in ASTM 119 Fire Resistance; PA1 2) transverse load strength as described in ASTM E72-80 in excess of 39 pounds per square foot and PA1 3) flame spread index of less than 25 as described ASTM El 62.
The stoppings also must provide a substantially air tight wall for closing-off of mine galleries, which results in passageways primarily used to direct air flow within the mine. Masonry walls are sealed with an overcoat. However, conventional concrete-block stoppings are often damaged by strata movement after installation. The damage may result in cracks in the blocks and joints which allows air to pass freely.
Accordingly, there is a need in the art for an improved apparatus and method for closing-off mine galleries.